Narrator: This is Science Today. For years, doctors have believed that estrogen plays a large role in determining who gets breast cancer. Now, studies have shown that higher levels of estrogen are linked closely with a higher risk. Dr. Steven Cummings of the University of California, San Francisco, says for post-menopausal women, an increase in estrogen is the best predictor of the disease.Cummings: If you take estrogen therapy, for example, your estrogen levels are… way out there…because estrogen therapy does increase your estrodial concentration about 5 to 10 fold more than natural post-menopausal levels. Narrator: Estrogen levels drop dramatically at menopause in all women. But Cummings says those with the very lowest levels of estrodial-the strongest form of the hormone-have by far the lowest risk of developing breast cancer. Cummings: If someone's breast cancer risk… is really low because they have low estrogen levels, what do you expect if they start taking estrogen therapy? …Their risk will go up.
Narrator: For Science Today, I'm Larissa Branin.